Fix incorrect unsupported error on synthetic extension call on LHS of ::

#KT-13271 Fixed

compiler/frontend/src/org/jetbrains/kotlin/resolve/calls/CallCompleter.kt

@@ -29,6 +29,7 @@ import org.jetbrains.kotlin.resolve.BindingContext.CONSTRAINT_SYSTEM_COMPLETER
 import org.jetbrains.kotlin.resolve.calls.callResolverUtil.ResolveArgumentsMode.RESOLVE_FUNCTION_ARGUMENTS
 import org.jetbrains.kotlin.resolve.calls.callResolverUtil.getEffectiveExpectedType
 import org.jetbrains.kotlin.resolve.calls.callResolverUtil.isInvokeCallOnVariable
+import org.jetbrains.kotlin.resolve.calls.callUtil.isCallableReference
 import org.jetbrains.kotlin.resolve.calls.callUtil.isFakeElement
 import org.jetbrains.kotlin.resolve.calls.checkers.CallChecker
 import org.jetbrains.kotlin.resolve.calls.checkers.CallCheckerContext
@@ -175,7 +176,7 @@ class CallCompleter(
         val returnType = candidateDescriptor.returnType
 
         val expectedReturnType =
-                if (isResolvingCallableReference(call)) {
+                if (call.isCallableReference()) {
                     // TODO: compute generic type argument for R in the kotlin.Function<R> supertype (KT-12963)
                     // TODO: also add constraints for parameter types (KT-12964)
                     if (!TypeUtils.noExpectedType(expectedType) && expectedType.isFunctionType) getReturnTypeFromFunctionType(expectedType)
@@ -241,11 +242,6 @@ class CallCompleter(
         setResultingSubstitutor(system.resultingSubstitutor)
     }
 
-    private fun isResolvingCallableReference(call: Call): Boolean {
-        val callElement = call.callElement
-        return (callElement.parent as? KtCallableReferenceExpression)?.callableReference == callElement
-    }
-
     private fun <D : CallableDescriptor> MutableResolvedCall<D>.updateResolutionStatusFromConstraintSystem(
             context: BasicCallResolutionContext,
             tracing: TracingStrategy

compiler/frontend/src/org/jetbrains/kotlin/resolve/calls/util/callUtil.kt

@@ -229,6 +229,12 @@ fun Call.isSafeCall(): Boolean {
 
 fun Call.isExplicitSafeCall(): Boolean = callOperationNode?.elementType == KtTokens.SAFE_ACCESS
 
+fun Call.isCallableReference(): Boolean {
+    val callElement = callElement
+    return callElement is KtNameReferenceExpression &&
+           (callElement.parent as? KtCallableReferenceExpression)?.callableReference == callElement
+}
+
 fun Call.createLookupLocation(): KotlinLookupLocation {
     val calleeExpression = calleeExpression
     val element =